Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen with a graphical user interface in portrait mode showing an embodiment of our new design.

FIG. 2 is a front view of a display screen with a graphical user interface in portrait mode showing an embodiment of our new design.

FIG. 3 is a front view of a display screen with graphical user interface in landscape mode showing an embodiment of our new design; and,

FIG. 4 is a front view of a display screen with graphical user interface in landscape mode showing an embodiment of our new design.

The broken lines showing a display device illustrate an environment. The broken line portions of the Figures, including broken line portions of display screens, broken line text, and broken line graphical elements form no portion of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 